Original subtitles

Bear: Three days of digging

And this olive ridley turtle is free,

But not safe, until she gets to the sea,

Where early life evolved and

Where nearly 80% of animals still live.

Of all the hatchlings born this year on the costa rican coast,

Only 10% will make it.

# #

Now she's in her element.

But her journey has just begun.

In ten years' time, she will return to these shores

To lay eggs of her own,

If she survives.

The ocean is a fluid and unpredictable world,

And all those that live here are at its mercy.

(theme music plays).

Our planet's oceans cover 70% of its surface,

And provide an incredible 99% of its habitable space.

This may be an alien world to us,

But it's home to an extraordinary range of animals,

From the biggest,

To the strangest creatures in our world.

Even for the most marine adapted,

Life isn't easy.

Survival at sea is a completely different game

To survival on land,

Especially when the rules keep changing.

Where the atlantic and indian oceans meet,

New conflicts between old foes are brewing.

Rising sea temperatures are pushing fish eastward

To cooler waters.

Those that feed on them have followed.

Fur seals.

Their new home is treacherous,

And it's not just the waves,

It's what lies beneath.

Not the best place to learn to swim,

But the perfect hunting ground for a great white shark.

This pup has strayed too close to the edge.

Now it's out of its depth.

A pup can outmaneuver a shark,

But only for so long.

Half of all such encounters end badly for seals.

(barking).

The adults must deal with this persistent menace,

But how?

It takes one brave seal to lead the way.

Others join.

Soon they are a mob, harassing the intruder.

It's a risky strategy; sharks can turn on a dime.

Together they have overcome a giant.

The pups are safe, at least for now.

Shallow continental seas are the most productive waters in

Our oceans.

They are also some of the most competitive.

During winter, these freezing fjords are the stage for one

Of the biggest wildlife spectacles on the planet.

This orca pod comes here every year.

They're led by a matriarch;

She could be 70 years old.

For a pod that specialize in hunting fish,

This is an unmissable event.

Herring.

Billions of them.

More fish here than people on the planet.

But the bigger the shoal,

The harder it is to single out a target.

The orca need to come at the problem from another angle.

Coordinating their attack, they divide and conquer.

Herders work to split the shoal.

Then in come the big hitters,

Slamming their tails, creating a shockwave,

Stunning up to 30 fish with each blow.

They must work quickly.

They're not the only hunters here.

Humpbacks, six times the weight of an orca.

They can devour more than 200 pounds of herring in one gulp.

The orca simply can't compete.

But they can switch tactic,

As long as they're prepared to face down

The most dangerous predator in the ocean.

Bear: In the ocean, where there is food,

There's usually a fight.

Off the fjords of norway, these orca are about to take

On the most aggressive ocean hunters of all,

Us.

Fishing boats like this can scoop up

800 tons of herring a day,

Out-fishing orca and humpbacks combined.

Desperation has forced these orca

To turn this new obstacle into opportunity,

Picking off the fish that slip through

Their competitors' nets.

Recently imposed quotas ensure there are enough herring for

Humans and whales.

But the global picture isn't so bright.

We are consuming more fish than ever before.

Reducing many stocks to little more than scales.

Unbalanced oceans are open to invasion,

By strange life forms.

They start life as pinhead sized polyps,

But what they lack in size they make up for in numbers.

Gorging on tiny plankton,

They grow, mutate and multiply

Into an army of clones.

Now each polyp becomes a production line

With one purpose.

Creating new jellyfish.

Bodies that are 95% water

Can easily grow and grow,

Until they are monsters.

No bones, no blood or even brains,

But perfectly suited to today's transforming seas.

Resistant to increasing temperature,

Decreasing oxygen, changing salinity,

Rising acidity, even plastic pollution.

When a jellyfish swarm takes over,

Some ecosystems never fully recover.

Our impact also extends to the biggest marine habitat of all.

The open ocean.

It covers more than half the globe,

But food here is increasingly scarce.

Yet one animal perseveres, despite needing

One and a half million calories every day.

The blue whale, the largest animal ever to have lived.

She's as long as an 18 wheeler,

With a heart as big as a car

And a tongue that weighs as much as an elephant.

Just this year, she's swum far enough to have

Circumnavigated the globe.

All in search of this.

Krill.

One of the most important species

In the marine food chain.

With each monumental gulp, she takes in enough water and

Krill to fill a school bus.

Her tongue forces the water back out through the bristly

Plates on her jaw, trapping up to two million krill.

Blue whales were hunted to the brink of extinction.

Although they're still endangered,

Since a ban on whaling in the 1960s,

Their numbers have increased worldwide,

And here, off the coast of california,

They have almost completely recovered.

The vast, open ocean can be a lonely place.

This green turtle has spent 30 years out here on her own.

Somehow, she's found enough food to survive and grow.

Now she's ready to return home,

But it will be a dangerous journey.

It's the breeding season, and hundreds of turtles are

Gathering to try and win a partner.

Males mate about four times as often as females,

So she attracts a lot of interest.

This male is quick to latch on.

But the others won't give up without a fight.

Bear: Off the coast of malaysia,

It's green turtle breeding season.

This female has found a mate,

But other males are intent on splitting the pair.

Targeting the male's soft flesh,

They try to force him to let go.

But the female has the most to lose.

The fiercer the pursuit, the more oxygen she burns.

A stressed turtle can drown in minutes.

She's desperate to reach the surface and breathe,

But one challenger just won't give up.

The female is running on empty.

Finally, the intruder backs off just long enough.

She's safe, but in just a few weeks she will face the final

Hurdle in her epic struggle to continue her line.

Where the tropical sun meets the shallow seas,

You find the busiest ocean habitat of all:

Coral reefs.

They account for less than a thousandth of the sea floor,

But are home to a quarter of all marine species.

In this crowded and dangerous place,

Finding shelter is essential.

Some hide in the coral maze,

Others seek sanctuary in the shoal.

But neither tactic guarantees safety.

Lionfish are one of the most efficient killers on the reef.

Yet there is a far greater threat facing

All those who live here.

Our seas have been steadily warming for the past 75 years.

Now it's happening faster than ever before.

It's having a profound impact on life throughout our oceans.

Coral reefs are particularly vulnerable.

Just a 3 degree temperature rise is too much for coral.

It forces them to expel the algae that feed them

And give them their color.

This bleaching is the first step towards an

Almost irreversible demise.

Unless temperatures drop, the reef becomes a wasteland.

In three decades,

We've lost over a quarter of the world's corals,

Home to around 4000 species of fish.

If warming continues, we could lose the rest.

Even those that live far below aren't safe from

Rising ocean temperatures.

Opalescent squid.

In the past few years, warming seas disrupted their mating

Habits, and their numbers have fallen dramatically.

But this year, an influx of cold water has revived

Their breeding ritual.

A trip to the shallows to mate by moonlight.

Males grab the females and fertilize their eggs,

Which are then deposited on the sea floor.

It's a brief and brutal affair.

Within days of mating they will all die.

But their legacy lives on.

Each capsule contains up to 300 new lives.

One successful breeding season can go a long way towards

Reversing their recent bad fortunes.

Those still alive retreat back to a place beyond

The reach of the sun,

Where crushing pressures have morphed bodies,

Into the stuff of nightmares.

Bear: To reach one of the most hostile environments on earth,

You must descend thousands of feet,

Beyond the sun's reach, down into the ocean's depths.

The pressure here would crush you like a soda can.

There is life, just not as we know it.

75% of animals make their own light.

Eyes are super-sized

To catch what tiny luminescence there is,

And soft bodies dominate.

In this vast, abyssal wilderness,

One of the toughest trials is finding a mate.

Angler fish have a grizzly solution.

This giant female's tiny hanger-on

Is a male angler fish.

Many males never find a mate.

Those that do, never let go.

His mouth fuses with her very tissue.

His only nourishment, her blood.

Bonded for life.

This alien environment is full of surprises.

It even snows down here.

Flakes of organic matter fall for weeks

Towards the sea floor.

Along the way, they fuel an ecosystem of

Microscopic animals and graceful giants.

The stygiomedusa jellyfish.

Its ribbon-like arms extend up to 30 feet to absorb tiny

Planktonic creatures, or so we believe.

Even today, the lives of these deep-sea monsters

Remain shrouded in mystery.

But the biggest surprise of all,

This marine underworld is one of the most

Stable habitats on the planet,

Out of touch with what's happening far above.

The sun has fueled a monster.

It heats surface waters until they evaporate and build into

Oceanic storms that render humans powerless.

And when conditions are just right,

They grow into one of the most formidable forces

On the planet:

Hurricanes.

They form over tropical seas,

Then their devastation spreads.

They release so much energy that just one could power

Our entire planet for a week.

And as global temperatures rise,

Hurricanes are growing stronger.

This is the calm before the storm.

Most people are already taking shelter.

But just off shore, others are on the move.

Mullet in their millions.

Few have heard of it, but this is one of the

Largest gatherings of any animal in the united states.

The mullet need to reach their spawning grounds

Further south before temperatures drop too low.

Such a mass of fish in the sea doesn't go unnoticed.

Expert hunters attack the shoal from every angle.

Below are the tarpon and blacktip sharks.

Above, pelicans, and osprey.

As the waves are whipped up by the approaching storm,

The pendulum swings in the mullet's favor.

In the turbulent, shallow water,

They're harder to target.

Finally, the swells grow too powerful,

As the storm makes landfall.

Along the coast, ocean storms create some of

Nature's most awe inspiring wonders.

Nazar� in portugal

Sees some of the biggest waves in the world,

Towering as high as ten stories.

But the stormier our seas become,

The more those living on the coast suffer.

An island on the edge of existence.

Home to rockhopper penguins.

A dense layer of fat gives them some protection.

Still they take a battering.

This mother can't back out now.

Her chick needs food.

And its dad's turn to hold the fort.

Life in the colony is tough.

Declining fish stocks and rougher seas

Have made food harder to come by.

Mum has to hunt,

And what was already a rough sea

Is about to get a whole lot rougher.

The most powerful storm in almost 30 years is closing in.

Worse than anything these penguins have faced before.

Bear: On the far south of the globe,

A brutal storm is finally subsiding.

But for these rockhopper penguins,

The waves are still deadly.

The latest shift of hunters returns.

But this chick's mum is nowhere to be seen.

Then, she appears.

Amongst the last stragglers.

# #

Home and dry.

(squawking, peeping).

In just 12 hours, she'll return to battle the waves.

And risk her life for her chick once more.

Right from the very beginning,

The ocean has been a cradle of life on our planet,

And the many creatures that still live here are

Really a legacy of that irrepressible will to

Succeed in a turbulent world.

No matter what the ocean has thrown at them,

Somehow they've managed to endure.

Against near impossible odds, this mum-to-be has found her

Way back to the beach where she was born.

It's the first time she's been on land

Since hatching over a decade ago,

And she's not alone.

Hundreds of thousands of female olive ridley turtles

Are returning to the costa rican coastline

To lay their eggs.

A cycle of life sustained by the sea for 30 million years.

Never has their journey been harder,

Yet so far, these turtles are still

Holding on in these fast changing times.

Captioned by cotter captioning services.